This project involves the investigation of the effects of accelerated heavy charged particles (such as neon and argon ions) on biological material. The research is intended to provide information both on the fundamental nature of the interaction of ionizing radiations with matter; and on the possible use of such heavy ions in treatment of human cancer. Studies include: effects on the survival of mammalian cells in tissue culture; effects on DNA-strand breakage; effects on various normal tissues of animals (skin, nervous system, lung, kidney), including both early and late responses; and effects on various experimental animal tumor systems. Assessment of effects of both single and multiple exposures to different heavy ions are made with the objective of defining potentially useful differential radiation responses between normal and tumor tissues, both in terms of initial effect and the ability of the exposed tissue to recover from radiation damage. Interpretation of biological effect in regard to the physical distribution of energy on the microscopic level is in progress. Bibliographic references: Leith, J. T., Schilling, W. A., Lyman, J. T., and Howard, J., Comparison of skin responses of mice after single or fractionated exposure to cyclothron-accelerated helium ions and 230-KV X-irradiation, Radiat. Res. 62, 195-215 (1975). Leith, J. T., Lewinsky, B. and Schilling, W. A., Modification of the response of mouse skin to X-irradiation by bleomcyin treatment, Radiat. Res. 61, 100-109 (1975).